The present invention relates to a magnetron unit with choke structures for reducing higher harmonics in microwave output.
It is well known that the magnetron unit oscillates at higher harmonic waves as well as at its a fundamental microwave frequency. When higher harmonic waves leak out of a microwave cooking oven into which the magnetron unit of such type is incorporated, there is fear that leaked harmonic energy may provide a health risk to users. In addition, leaked harmonic radiation may also interfere with telecommunication frequency channels to disturb communication.
For the purpose of preventing higher harmonic waves from being radiated from the output antenna section of magnetron unit, the conventional magnetron unit is provided with choke structures to suppress higher harmonic waves. U.S. Pat. No. 3,849,737, for example, discloses a magnetron unit provided with two choke structures comprising a metal evacuating tube of predetermined depth L.sub.1 and a metal cylinder of predetermined depth L.sub.2. However, one of the choke structures of this magnetron unit in which the metal cylinder is attached to an intermediate portion of an output conductor has a problem that it is mechanically unstable. In addition, there is a fear in it that high frequency discharge is caused between the metal cylinder and other parts of magnetron unit.